A teenage boy nearly died after vaping caused a catastrophic reaction in his lungs, doctors in Nottingham say.
Ewan Fisher was connected to an artificial lung to keep him alive after his own lungs failed and he could not breathe.
Ewan told BBC News e-cigarettes had "basically ruined me" and urged other young people not to vape.
His doctors say vaping is "not safe", although health bodies in the UK say it is 95% safer than tobacco.
Ewan started vaping in early 2017. He was 16 at the time and wanted to quit smoking to improve his boxing.
Despite being under age, he said, "it was easy" to buy either cigarettes or e-cigarettes.
In May that year, Ewan was finding it harder and harder to breathe.
His mother took Ewan to accident and emergency on the night before his GCSE exams, because he was coughing and choking in his sleep.
His lungs were failing and he very quickly ended up on life-support in intensive care in Queen's Medical Centre in Nottingham.
"I thought I was going to die," Ewan told BBC News.
Ewan was getting worse. Even ventilation could not get enough oxygen into his body and his life was in the balance.
He was taken to Leicester and attached to an artificial lung or ECMO (extra-corporeal membrane oxygenation) machine.
"This machine saved my life," he said.
Large tubes took blood out of Ewan, removed the carbon dioxide, added oxygen and pumped the blood back into his body.
"He had very serious respiratory failure, he had to go to ECMO and that is a very big deal," Dr Jayesh Bhatt, a consultant at Nottingham University Hospitals, told BBC News.
"He got as ill as anyone can get."
The case - from May 2017 - has just come to light in the journal Archives of Disease in Childhood.
How is Ewan now?
Ewan, who is 19 on Tuesday, had a long recovery. It was six months before he was properly up and on his feet again.
"I'm still not back to normal, I'd say 75-80%, it's in the last six months that I'm feeling a bit stronger in myself," he said.
"Vaping has basically ruined me, I try to tell everyone and they think I'm being stupid, I tell my mates and they don't listen.
"They still do it... but they've seen what I've been through.
"Is it worth risking your life for smoking e-cigs?
"I don't want you to end up like me and I don't want you to be dead, I wouldn't wish [that] on anyone."
Ewan also fears being around other vapers - everywhere from the pub to High Street - could damage his lungs again.
Is vaping to blame?
His doctors say the answer is yes.
Ewan developed a condition called hypersensitivity pneumonitis - something he was breathing in was setting off his immune system, with catastrophic consequences.
"You get an over-exuberant inflammatory response and the lungs pay a price and develop respiratory failure," Dr Bhatt said.
One of the most common forms of hypersensitivity pneumonitis is "bird fancier's lung", which is caused by particles from feathers or bird droppings.
When scientists tested the two e-cigarette liquids Ewan had been using, they found one of them was triggering an immune reaction.
Dr Bhatt said: "The real learning point is vaping is not safe, especially for young people, they should never go near it.
"We consider e-cigarettes as 'much safer than tobacco' at our peril."
How common is this?
There are 3.6 million people vaping in the UK and reactions like this are rare.
However, doctors have told BBC News Ewan's case is not an isolated incident.
"As vaping becomes more popular, we are beginning to see more cases," Dr Hemant Kulkarni, a consultant in paediatric respiratory medicine at Sheffield Children's NHS Foundation Trust, said.
He told BBC News: "Some of the cases my colleagues and I have seen are teenagers presenting with severe lung injury and some of these have been life-threatening.
"However, in the cases I've been involved in, patients are now regaining normal lung function."
Dr Kulkarni is "surprised" e-cigarettes are advertised in the UK, given the severe reaction they can cause in children and a lack of scientific studies on their safety.
Is vaping dangerous?
Smoking is pretty much the worst thing you can do for your health.
E-cigarettes are promoted in the UK as a way to quit because they let people inhale nicotine in vapour rather than breathing in smoke.
Ewan's reaction was extreme, but what about the rest of us who would not end up with hypersensitivity pneumonitis?
Public Health England says vaping is 95% safer than smoking but is not without risks.
Rosanna O' Connor, the body's director of drugs, alcohol and tobacco, said: "Smoking kills half of lifelong smokers and accounts for almost 220 deaths in England every day.
"Our advice remains that while not completely risk free, UK regulated e-cigarettes carry a fraction of the risk of smoked tobacco."
But there are arguments about how safe vaping really is.
The World Health Organization says e-cigarettes are "undoubtedly harmful and should therefore be subject to regulation".
It also raises concerns vaping is being aggressively marketed at young people - particularly through the use of flavourings - and risked re-normalising smoking.
Is Ewan's case similar to those in the US?
The deaths of 39 people in the US have been connected to vaping and have prompted worldwide concern about its safety.
There have been 2,051 cases of e-cigarette, or vaping, product use associated lung injury (called EVALI) in the outbreak.
Most of those cases, but not all, have been linked to vaping THC, the psychoactive ingredient in cannabis.
Ewan was using standard e-cigarettes bought from a shop.
What do experts says?
Dr Nick Hopkinson, medical director of the British Lung Foundation, said: "If people switch completely from smoking to vaping, they will substantially reduce their health risk as e-cigarettes do not contain tobacco and any harmful components are present at a much lower level.
"People who do switch should try to quit vaping in the long term too but not at the expense of relapsing to smoking - and non-smokers should not take up vaping."
Prof John Britton, the director of the UK Centre for Tobacco and Alcohol Studies, at the University of Nottingham, said: "This is worrying, and the risk needs to be acknowledged, but in absolute terms it is extremely small and, crucially, far smaller than that of smoking.
"The advice remains the same: if you smoke, switch to vaping; if you don't smoke, don't vape."
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